1. Field of the Invention
The present invention relates to a communication network system in which communication can be performed among a plurality of mobile terminals.
2. Description of the Related Art
Optical communication using infrared rays is being performed as a data communication interface for use in personal computers and mobile terminals including personal digital assistants (PDA). The infrared data association (IrDA) protocol is a standard protocol for infrared optical communications.
However, in infrared optical communication using this IrDA standard protocol, only a one-to-one-type communication function is supported. Thus, when a single one-to-one-type communication terminal communicates with a plurality of terminals connected via a local area network (LAN), it is necessary to connect at least one relay terminal having both the IrDA function and the LAN function to a LAN system circuit. Then, communication is performed via this relay terminal.
As in the IrDA communication interface, a data communication interface using a modem connected to a telephone line also supports only a one-to-one-type communication function. Terminals using IrDA or a modem and merely having a one-to-one-type communication function are hereinafter referred to as “one-to-one-type communication terminals”.
Such a one-to-one-type communication terminal can communicate with a plurality of terminals by the provision of a relay terminal which relays information of the one-to-one-type communication terminal to the other terminals. However, the following problems are encountered if IrDA is used as a communication interface.
If the relay terminal or the one-to-one-type communication terminal using IrDA is moved, the communication link may be disconnected. When the relay terminal discontinues relay services, the one-to-one-type communication terminal is no longer able to communicate with the other terminals.
However, even if the relay terminal is moved or the relay services are discontinued, the provision of an extra relay terminal which takes over the relay services in a network (LAN) makes it possible to continue relaying information of the one-to-one-type communication terminal, which can thus communicate with the other terminals.
However, the one-to-one-type communication terminal is not disposed in the network. It is thus impossible for the one-to-one-type communication terminal to monitor the situations of the terminals connected to the network nor can it check for the presence of another relay terminal in the network even if it attempts to send a relay request to the relay terminal.
Similarly, in performing communication using a modem, problems similar to those presented by IrDA communication may be encountered if relay services are discontinued or a telephone line is disconnected, thereby discontinuing communications between a one-to-one-type communication terminal using a modem and other terminals. There may be provided a mechanism for indicating another relay terminal which takes over relay services before the corresponding relay terminal discontinues the relay services. Even in this case, if a communication link is accidentally disconnected for a one-to-one-type communication terminal using IrDA, or if a telephone line is disconnected for a one-to-one-type communication terminal using a modem, communication can no longer be performed.
Even if the relay services are successfully passed from one relay terminal to another relay terminal, the one-to-one-type communication terminal first sends a connection request to the indicated relay terminal, and then, after a communication link is established, the one-to-one-type communication terminal is able to receive the relay services. In other words, the one-to-one-type communication terminal is unable to receive information sent to this terminal until the communication link with the designated relay terminal is established.
Additionally, a one-to-one-type communication terminal using a modem cannot even be connected to a relay terminal while the relay terminal has already started to provide relay services. If only one telephone number of the relay terminal is known to the one-to-one-type communication terminal, the terminal cannot even be connected to the relay terminal, thus failing to receive the relay services.
The aforementioned IrDA communication interface and the modems are major communication interfaces for use in mobile personal computers and mobile terminals. Thus, the above-described problems are becoming serious as mobile computing is becoming widespread and is more commonly utilized.
Therefore, in communicating with a plurality of terminals via a relay terminal, even if a one-to-one-type communication terminal becomes unable to communicate with the relay terminal, the communication must be continued by passing relay services from the relay terminal to another relay terminal disposed in a network.